1. Field of the Invention
The present invention relates a printed laminated circuit board, and more particularly to a vertical conductive unit and a manufacturing method thereof.
2. Description of the Related Art
Because of being high in wiring density, light, and small in size, printed circuit boards are important electronic parts of various electronic appliances and widely applied in products such as notebook computers, mobile phones, digital cameras, and liquid crystal displays.
In the trend that electronic products are becoming lighter and thinner and have multiple functions, a non-mechanical drilling lamination method for manufacturing a micro via with the diameter smaller than about 5 micro-meters of a printed circuit board comprising has been developed. The micro via combines with fine wires and short spacing to achieve high density interconnection (HDI). The blank micro via obtained according to the method may be further subjected to various metallization and copper electroplating processes to achieve a blind via or a buried via that is locally interlayer-interconnected. The micro via may also be filled with a silver paste or a copper paste to replace the difficult metallization and copper electroplating processes to achieve electrical connection, and an insulating layer is required to be provided between layers.
However, miniaturization of the printed circuit board faces many challenges. When a digital signal or an analog signal enters a high speed or high frequency (for example, radio frequency (RF) or microwave) environment, electromagnetic interference (EMI), radio frequency interference (RFI), and other various noise interferences are increasingly serious. When two parallel wires in a wiring network of the printed circuit board incur near end crosstalk or coupling, the following methods are applied: (1) installing a decoupling capacitor or enlarging the spacing between the wires, but under the requirement of dense wiring, only the parallel length thereof can be decreased to reduce mutual inductance of a magnetic field and mutual capacitance of an electric field; or, (2) decreasing the thickness of the insulating layer to enable crosstalk energy to be grounded.
In order to make the micro via, multiple non-mechanical drilling methods are developed. For example, IBM developed a surface laminar circuits (SLC) photo-via technology in the YASU factory in Japan in 1989; then, laser ablation, plasma via-etching, dry via-etching, and wet chemical via-etching followed. According to the photo-via technology, a photosensitive resin undergoes a photographic imaging process, and the micro via is formed through steps such as exposure and development. However, besides photosensitive property, other properties of the photosensitive resin such as desirable electric properties, desirable mechanical properties, chemical resistance for the photographic imaging process, and high heat resistance for a lamination process are required.
For example, for the desirable electric properties, the breakdown voltage (dielectric Strength) needs to bear a basic 2 KV voltage, and the breakdown voltage relates to the thickness of the insulating layer. A currently applied photosensitive insulating layer is an epoxy resin, but in order to meet the requirement of breakdown voltage, the thickness of the epoxy resin shall be at least greater than 50 μm. Many polymers having desirable electric properties must be pressed in the lamination process only under a high temperature because the glass transition temperature (Tg) thereof is too high, which makes the application difficult.
On the other hand, for the laser ablation or plasma via-etching method, when a layer is added, an adhesive layer, which is generally an epoxy resin, is additionally required, so that the thickness of the insulating layer thereof is at least greater than 32 μm.
Further, referring to FIG. 1, in order to manufacture a conventional printed laminated circuit board 1, a first wiring layer 11 is provided first, and a first circuit 12 is formed on the first wiring layer 11. Then, the first circuit 12 is covered by an insulating first cover film 13 that is mechanically punched. In order to further perform lamination, an adhesive layer 14 is provided; then a second wiring layer 15 is placed on the adhesive layer 14. Further, a second circuit 16 is formed; then the second circuit 16 is covered by a second cover film 17. In order to enable the first circuit 12 and the second circuit 16 to be electrically connected, a via needs to be formed through the first cover film 13, the adhesive layer 14, and the second wiring layer 15 through laser ablation; then a connecting conductor 18 is formed in the via through filling, chemical plating or electroplating, to connect the first circuit 12 and the second circuit 16. Then, the second circuit is used as another first circuit, the second cover film is used as another first cover film, and the aforementioned steps, such as providing a wiring layer, forming a circuit, using a cover film for coverage, using an adhesive layer for adhesion, ablation, and forming a connecting conductor are repeated, so as to manufacture the conventional printed laminated circuit board 1. The manufacturing method cannot decrease the overall thickness of the printed laminated circuit board, and the complicated manufacturing processes increase the difficulty in manufacturing. Furthermore, it is not easy to align multiple layers, which results in that a short circuit phenomenon is likely to be incurred. Moreover, when the first cover film 13 and the second cover film 17 cover the first circuit 12 and the second circuit 16, or when the adhesive layer 14 performs adhesion, a high-temperature pressing is required, which increases the difficulty of the process.
Therefore, in the field, a novel printed laminated circuit board and manufacturing thereof urgently need to be provided, so as to meet requirements incurred by development of electronic appliances.